Solid alpha-olefin polymerization catalyst components

ABSTRACT

A process for preparing a solid catalyst component which comprises halogenating a magnesium compound in the formula MgRR 1 .nCO 2  l in which R and R 1  are the same or different alkoxy or phenoxy groups and n is a number of from 0 to 2 with a halide of tetravalent titanium in the presence of dialkylester of a dihydric aromatic carboxylic acid and an inert hydrocarbon diluent by reacting at a temperature of from 120° to 136° C. and recovering the solid reaction product from the reaction mixture.

This invention relates to solid alpha-olefin polymerization catalystcomponents and a process for preparing the same.

It is known to provide alpha-olefin polymerization catalysts bycombining a solid component comprising at least magnesium, titanium andhalogen with an activating organoaluminium compound. These may bereferred to as supported coordination catalysts or catalyst systems. Theactivity and stereospecific performance of such compositions aregenerally improved by incorporating an electron donor in the solidcomponent--this electron donor sometimes being referred to as "innerdonor"--and by employing as a third catalyst component an electron donorwhich may be complexed in whole or in part with the activatingorganoaluminium compound, the latter electron donor sometimes beingreferred to as "outer donor" or "selectivity control agent" (SCA).

Supported coordination catalysts of this type are generally able toproduce olefin polymers in high yield and, in the case of catalysts forpolymerization of propylene or higher alpha-olefins, with highselectivity to stereoregular polymer cf. GB 1,389,890 and GB 1,559,194.However, they tend to lose their advanced polymer productivity rateafter a fairly short period of time. This negative phenomenon is knownas "decay", c.f. L. Luciani, Angew. Makromol. Chemie, 94 (1981), p.63-89, FIGS. 14 and 15.

EP 45,977 is concerned with a catalyst system having a reduced decayrate. That system comprises a solid catalyst component based onmagnesium halide, titanium halide and di-isobutyl phthalate and aco-catalyst comprising trialkyl aluminium which is complexed with i.a.phenyltriethoxysilane. The hygroscopic character of the magnesiumdichloride starting material used to produce the solid catalystcomponent is one of the disadvantages of that known catalyst system.

The problems related to hygroscopic nature of the starting material areavoided when employing the solid catalyst system known from EP 19,330.In that event the starting material is magnesium dialkoxide ordiphenoxide which is converted into magnesiumdichloride by halogenatingwith titanium tetrachloride in the presence of an electron donor and ahalohydrocarbon. The latter serves to reduce by extraction the contentof soluble TiCl₄ --electron donor complex in the solid catalystcomponent so produced, the said reduction being associated with animprovement in catalytic performance. This known catalyst is once againof the fast-decaying type and the prescribed need to employhalohydrocarbons will pose waste-stream disposal problems in catalystmanufacture. Surprisingly, it has been found that by effecting theaforesaid known halogenation method at temperatures markedly higher thanthose known from EP 19,330, it is possible to prepare solid catalystcomponents from magnesium alkoxide or phenoxide starting materials whichin combination (1) provide a solution to the decay problem; (2) do awaywith the halohydrocarbon disposal problem and (3) which in terms ofpolymerization performance (polymer yield) are dramatically superior tothe catalysts disclosed in EP 19,330.

The present invention provides a process for preparing a solid catalystcomponent which comprises halogenating a magnesium compound of theformula MgRR¹.nCO₂ in which R and R¹ are the same or different alkoxy orphenoxy groups and n is an integer of from 0 to 2 with a halide oftetravalent titanium in the presence of a dialkylester of a dihydricaromatic carboxylic acid and an inert hydrocarbon diluent by reacting ata temperature of from 120° to 136° C. and recovering the solid reactionproduct from the reaction mixture.

In the halogenation reaction of the invention suitable magnesiumcompounds to be employed as starting materials are compounds likemagnesium dimethoxide, magnesium diethoxide, methoxy magnesiumphenoxide, magnesium diphenoxide, methoxy magnesium ethoxide, magnesiumdibutoxide and isopropoxy magnesium phenoxide. The aforesaid phenoxygroups may comprise one or more halogen or alkoxy substituents. All ofthe just listed compounds are compounds of the general formula markedabove, in which n equals zero. Magnesium diethoxide and magnesiumdiphenoxide are preferred starting materials.

In another preferred group of starting materials n does not equal zero.In such compounds the CO₂ moiety is predominantly present in the form ofat least one carbonate linkage ##STR1## in which 'R stands for alkyl,aryl, dihalo- or dialkoxy substituted phenyl. They can be prepared bycontacting a dispersion of the defined MgRR' compound in a suitablediluent with carbon dioxide. It is preferred that the carbon dioxide be99.8% or more pure CO₂. Typically, the CO₂ is bubbled through thedispersion of magnesium compound in a diluent. Since the reaction isexothermic, one may continue bubbling the CO₂ until the exotherm hasended and the solid compound dissolves. The diluent employed may be anymaterial in which the carbonated magnesium compound is soluble atdesired conditions. Preferred diluents are alcohols. However, otherpolar solvents such as acetone or dimethyl formamide (DMF) may be used,as well as mixed solvents. Preferably, when an alcohol is employed it isused in conjunction with a magnesium compound containing two of the samegroups, i.e. an alcohol of formula ROH is used with a magnesium compoundof formula Mg(OR)₂. For example, if magnesium diethoxide is used, thenit is preferred that the diluent be ethanol. The desired magnesiumcompound can be recovered in solid form from the solution by spraydryingto obtain adequate morphology control.

In the halogenation with a halide of tetravalent titanium, the magnesiumcompounds are preferably reacted to form a magnesium halide in which theatomic ratio of halogen to magnesium is at least 1.2/1. Better resultsare obtained when the halogenation proceeds more completely, i.e.yielding magnesium halides in which the atomic ratio of halogen tomagnesium is at least 1.5/1. The most preferred reactions are thoseleading to completely halogenated reaction products, i.e. magnesiumdihalides. Such halogenation reactions are suitably effected byemploying a molar ratio of magnesium compound to titanium compound of0.0005:1 to 2:1, preferably 0.01:1 to 1:1. In this invention thehalogenation reaction is conducted in the additional presence of adefined electron donor. A liquid inert hydrocarbon diluent is preferablyalso present. Preferred diluents are aromatic hydrocarbons, such asxylene or ethylbenzene.

Suitable halides of tetravalent titanium include aryloxy or alkoxy-di-and trihalides, such as dihexanoxy-titanium dichloride,diethoxy-titanium dibromide, isopropoxy-titanium tri-iodide andethoxytitanium trichloride, and titanium tetrahalides. The tetrahalidesare preferred, most preferred is titanium tetrachloride.

The electron donors may be chosen from the esters of phthalic acid,terephthalic acid, 1,4-naphthalene dicarboxylic acid, naphthalic acidand 1,2- or 2,3-naphtha lene dicarboxylic acid. Phthalic acid esters andin particular the C₃ to C₁₀ alkyl esters thereof are preferred. Thus,very good esters are di-isoheptyl-, di-2-ethylhexyl-, di-isooctyl-,di-n-pentyl-, di-n-nonyl, di-2-methyl-3-ethylpentyl-, di-isobutyl- anddi-n-butyl-phthalate.

The halogenation proceeds under formation of a solid reaction productwhich may be isolated from the liquid reaction medium by filtration,decantation or another suitable method and may be subsequently washedwith an inert hydrocarbon diluent, such as n-hexane or iso-octane, toremove any unreacted material, including physically absorbed aromatichydrocarbon diluent.

Subsequent to halogenation, the solid product may be contacted with ahalide of tetravalent titanium, e.g. a dialkoxy-titanium dihalide, aphenoxy titanium-trihalide, a dichloro-phenoxy titaniumtrihalide ortitanium tetrahalide in order to increase the titanium content of thesolid catalyst component. This increase should preferably be sufficientto achieve a final atomic ratio of tetravalent titanium to magnesium inthe solid catalyst component of from 0.005:1 to 3.0:1, particularly offrom 0.02:1 to 1.0:1. To this purpose the contacting with the halide oftetravalent titanium is most suitably carried out at a temperature offrom 60° C. to 136° C. for 0.1-6 hours. Particularly preferredcontacting temperatures are from 120° C. to 136° C. and the mostpreferred contacting periods are 0.2 to 2 hours. This treatment may becarried out in repeated contacts of the solid with separate portions ofthe halide of tetravalent titanium, optionally in the presence of aninert hydrocarbon diluent.

Three basic features distinguish the present novel preparation processfrom the prior art method known from EP 19,330

(a) the use of different electron donors;

(b) the use of higher temperature during halogenation; and

(c) the absence for the need for copresence of a halohydrocarbon duringhalogenation.

Whilst the presence of minor amounts of halohydrocarbon duringhalogenation in accordance with this invention can be tolerated, nobeneficial effects are obtained therewith. Consequently, in order tosimplify the working up, recycling or disposal of titaniumhalidewaste-streams, it is preferred to carry out the halogenation in theabsence of halohydrocarbon.

In the end, the catalyst component is suitably washed to removeunreacted titanium compound. The titanium content of the final, washedsolid catalyst component is suitably 1.5 to 3.6 percent by weight, butcan be up to 4.5 percent by weight. The material used to wash thecatalyst component suitably is an inert, light hydrocarbon liquid.Preferred light hydrocarbon liquids are aliphatic, alicyclic andaromatic hydrocarbons. Examples of such liquids include iso-pentane,n-hexane, iso-octane and toluene, with iso-pentane being most preferred.

For the polymerization of alpha-olefins the solid catalyst component isemployed in conjunction with an organo aluminium compound and,optionally, any one of the electron donors set out hereinbefore. Moresuitable electron donors are organic silicon compounds includingalkoxysilanes and aryloxysilanes of the general formula S¹ Si(OS²)_(4-n)where n is between zero and three. S¹ is a hydrocarbon group or ahalogen atom and S² is a hydrocarbon group. Specific examples includetrimethylmethoxysilane, diphenyldimethoxysilane, dimethyldimethoxysilaneand phenyltriethoxysilane. A stericallly hindered amine such as2,2,6,6-tetramethylpiperidine (TMP) may also be used. Preferredselectivity control agents are TMP, phenyltriethoxysilane anddiphenyldimethoxysilane.

The organoaluminium compound to be employed as cocatalyst may be chosenfrom any of the known activators in olefin polymerization catalystsystems comprising a titanium halide. While trialkylaluminium compounds,dialkylaluminium halides and dialkylaluminium alkoxides may be used,trialkylaluminium compounds are preferred, particularly those whereineach of the alkyl groups has 2 to 6 carbon atoms, e.g.triethylaluminium, tri-n-propylaluminium, triisobutylaluminium,triisopropylaluminium and dibutyl-n-amylaluminium.

Preferred proportions of selectivity control agent, employed separately,in combination with, or reacted with an organoaluminium compound, arefrom 0.005 to 1.5, particularly from 0.1 to 0.8, calculated as mol permol aluminium compound . Preferred proportions of selectivity controlagent calculated as mol per mol titanium are from 0.1 to 50,particularly from 0.5 to 20.

Proportions of electron donor contained in the solid catalyst component,calculated as mol per mol of magn®sium, are suitably from 0.01 to 10,e.g. from 0.05 to 5.0 and especially from 0.05 to 0.5.

To prepare the final polymerization catalyst composition, the solidcatalyst component, organoaluminium compound and selectivity controlagent, if used, may be simply combined, most suitably employing a molarratio to produce in the final catalyst an atomic ratio of aluminium totitanium of from 1:1 to 150:1. The catalysts of this invention tend toexhibit very good activity at low Al:Ti ratios, e.g. below 80:1. It may,however, be advantageous under some conditions to employ at higher Al:Tiratios even up to 500:1. Increasing the Al:Ti ratio tends to increasecatalyst activity at the expense of increased catalyst residue in theunextracted product. These factors, as well as the desired level ofisotacticity, will be considered in selecting the Al:Ti ratio for anygiven process and desired product. In general, Al:Ti atomic ratios offrom 30:1 to 100:1 will be preferred.

The present invention is also concerned with a process for polymerizingan alpha-olefin, e.g. 1-hexene, 1-butylene or more preferably propylene.These polymerizations may be carried out by any of the conventionaltechniques, such as gas phase polymerization or slurry polymerizationusing liquid monomer or an inert hydrocarbon diluent as liquid medium.

The invention is further illustrated by working examples.

EXAMPLE

4 g Magnesium-diethoxide was heated during 1.5 hr at varying temperatureunder stirring with 80 ml TiCl₄ /aromatic solvent mixture (v:v=50:50)and 2 ml diisobutyl phthalate (ester/Mg molar ratio 0.22). The liquidphase was removed by filtration while hot, and two additional treatmentswith TiCl₄ /solvent were carried out, each during 0.5 hr and at the sametemperature as employed before. The final solid product was washed with50 ml isooctane (6x) and kept for further use as a suspension in mineraloil.

Propylene was polymerized in a liquid bulk reaction (propylene monomer)under the following standard conditions: T=67° C., period 1 hr, pressure700 kPa, TEA/Ti molar ratio 150:1 (TEA=triethylaluminium), TEA/TMP molarratio 2.5:1 (TMP=2,2,6,6-tetramethylpiperidine), H₂ concentration 1.5%vol in gas cap, solid catalyst component:20 mg.

With various inert hydrocarbon diluents and different reactiontemperatures for halogenation the following polymerization data markedin Table I, in terms of polymer yield (kg polymer per g cat. component)and xylene solubles (XS, % w), were obtained.

                  TABLE I                                                         ______________________________________                                        Diluent        T, °C.                                                                             Yield   XS                                         ______________________________________                                        Xylene         120         32      4.4                                          "            130         48      4.5                                          "            135         38      5.5                                        Ethylbenzene   120         31      4.8                                          "            130         39      3.9                                          "            135         36      5.5                                        monochlorobenzene*                                                                           100         23      5.8                                        monochlorobenzene**                                                                           80         18      6.3                                        ______________________________________                                         *for comparison, solid component having been prepared by substituting         monochlorobenzene for xylene in both halogenation and each of the             subsequent TiCl.sub.4 treatments, all other conditions left unchanged.        **for comparison, as in * but now employing phenyltriethoxysilane (PTS) i     stead of TMP in cocatalyst (TEA/PTS molar ratio 10:1).                   

We claim:
 1. A process for prepating a solid catalyst component whichcomprises halogenating a magnesium compound of the formula MgRR¹.nCO₂ inwhich R and Rhu 1 are the same or different alkoxy or phenoxy groups andn is a number of from 0 to 2 with a halide of tetravalent titanium inthe presence of dialkylester of a dihydric aromatic carboxylic acid andan inert hydrocarbon diluent by reacting at a temperature of from 120°to 136° C. and recovering the solid reaction product from the reactionmixture.
 2. A process as claimed in claim 1 wherein the dialkyl ester isa C₃ to C₁₀ alkyl ester.
 3. A process as claimed in claim 1 wherein thearomatic carboxylic acid is phthalic acid.
 4. A process as claimed inclaim 1 wherein the halogenation reaction is effected in the presence ofa liquid aromatic hydrocarbon.
 5. A process as claimed in claim 4wherein the reaction is effected in the absence of a halohydrocarbon. 6.A solid catalyst component whenever obtained with a process as claimedin claim
 1. 7. A catalyst for the polymerization of alpha-olefinscomprising a solid catalyst component as claimed in claim 6, anorganoaluminium compound and a soluble control agent.